We are developing superconducting magnets for MRI with Re1Ba2Cu3O7-δ (Re: rare earth, Y, Gd, Eu, REBCO) tapes. Superconducting magnets for MRI need the uniformity of the produced magnetic field in time and space. The disturbance is mainly caused by the induced shielding current in the wound superconducting tapes, which corresponds to the magnetization of the REBCO superconducting tapes. We have made a test coil with REBCO tapes and evaluated the influence of the shielding current on the produced magnetic field. In this paper, applying external magnetic field perpendicular to the EuBCO superconducting tape face, we investigated the magnetization and its relaxation properties of the tapes at 20-40 K using a saddle-shaped pickup coil. Increasing an applied magnetic field and interrupting the field sweep temporarily at 0, 0.5, 1, 1.5, 2, and 2.5 T, we observed the variation of the magnetization for each step of magnetic field. The magnetization decayed at a speed of a few to tens of percent per minute. It was faster beyond expectation. The relaxation rate of the magnetization depended on magnetic field, temperature, and the number of stacked tapes. It became faster with increasing temperature and magnetic field and with decreasing number of stacked tapes.
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